Migadu and Fastmail are good alternatives in case hosting your own is too much effort. I got bitten by the same issue with the lack of IMAP when moving to Tutanota, another secure email provider.
I run my personal email on Fastmail, but I don't like the idea of them being compelled to turn over my entire mailspool on demand to intelligence agencies without a warrant, so I'll go back to hosting my own, as I did for 20 years before Fastmail. :/
That is one of the reasons I switched to Migadu. The other being cost, as I have several domains that receive very little mail, so the cost structure on Migadu is very attractive.
Just get a small hosting package from Hetzner. 3 Euro/month and you are done. Comes with a free tld, too.
Isn't Hetzner heavy blocked by the large mail providers? I had similar issues with Digital Ocean, AWS, Linode etc when trying to self host. Even tried smarthosting via SES and that still made my very small volume of emails land in spam folders.
Hm, not sure, haven't heard anything like that. Try netcup.de. I'm with them and I'm happy, mail also works without problems.
In fact, they provide an imap bridge for paid customers.
I know, I use it (and have recompiled it to patch out the mangling of incoming PGP messages).